This invention relates to a cap for venting a tank containing a fluid, such as for example a volatile liquid, and for preventing the tank from exploding upon the fluid in the tank expanding in response to externally applied heat.
Caps are known to the art for venting a tank to the atmosphere and for preventing the tank from exploding upon the fluid contained in the tank expanding in response to externally applied heat. Such prior art caps typically include an outer annular nut, an inner or circular central disc, and an annular ring of a fusible low melt alloy intermediate and interconnecting the outer annular nut and the inner or circular central disc. Typically such fusible low melt alloys contain lead and a commonly used fusible low melt alloy containing lead is a lead-bismuth alloy. Such prior art caps are typically used to vent tanks such as, for example, trailer tanks, storage tanks, and intermediate bulk tanks. Such tanks contain, for example, petrochemical liquids, such as for example gasoline, and pharmaceutical and food grade liquids.
The use of the above-noted lead-based fusible rings has become objectionable due to the fact that the lead can possibly contaminate pharmaceutical and food grade liquids and the use of lead-based fusible rings is also objectionable due to the fact that upon disuse and disposal of a cap including the lead-based fusible ring in a land fill, for example, the lead in the fusible ring can contaminate the environment.
Accordingly, there is a need in the art for a cap which does not include lead and which cap can vent a tank to prevent the tank from exploding upon liquid contained in the tank expanding in response to externally applied heat.